1. Field of the Invention
The present invention relates to a pattern creating apparatus and a pattern creating method and, more particularly, to those suitably applicable, for example, to the design of circuit patterns of photomasks or reticles used in an exposure step to expose a photosensitive substrate to exposure light in a microscopic circuit pattern in production of various devices such as semiconductor chips including IC, LSI, and so on, display elements including liquid crystal panels etc., detecting elements including magnetic heads etc., image pickup elements including CCD etc., and so on.
2. Related Background Art
For manufacturing the devices such as the IC, LSI, liquid crystal panels, and so on by the photolithography technology, it was conventional practice to employ projection exposure to project a circuit pattern of a photomask or a reticle or the like (hereinafter referred to as xe2x80x9cmaskxe2x80x9d) onto a photosensitive substrate such as a silicon wafer or a glass plate or the like (hereinafter referred to as xe2x80x9cwaferxe2x80x9d) coated with a photoresist or the like by a projection optical system, so as to transfer (or expose) the circuit pattern thereonto.
In recent years, in response to the tendency toward higher integration of the above devices, there are demands for much finer patterns to be transferred onto the wafer, i.e., for increase of resolution to higher values. In the above projection exposure technology, which is the core of the micro-fabrication technology for wafers, therefore, the increase of resolution is now labored for forming an image (circuit pattern image) in the size (line width) of 0.3 xcexcm or less.
A schematic diagram of a conventional projection exposure apparatus is illustrated in FIG. 19. In FIG. 19, reference numeral 191 designates an excimer laser as a light source for deep ultraviolet exposure, 192 an illumination optical system, 193 illumination light emerging from the illumination optical system 192, 194 a mask, 195 object-side exposure light emerging from the mask 194 and then entering an optical system (projection optical system) 196, 196 a demagnification type projection optical system, 197 image-side exposure light emerging from the projection optical system 196 and then entering a substrate 198, 198 a wafer being a photosensitive substrate, and 199 a substrate stage for holding the photosensitive substrate.
The laser light emitted from the excimer laser 191 is guided to the illumination optical system 192 by a routing optical system (190a, 190b) and is regulated by the illumination optical system 192 so as to be the illumination light 193 having predetermined light intensity distribution, distributed light distribution, spread angle (numerical aperture NA), etc., which illuminates the mask 194. In the mask 194 a pattern is made of chromium or the like on a quartz substrate and in the size equal to the inverse of a projection magnification of the projection optical system 196 (for example, two, four, or five) times a microscopic pattern to be formed on the wafer 198. The illumination light 193 is transmitted and diffracted by the microscopic pattern of the mask 194 to become the object-side exposure light 195.
The projection optical system 196 converts the object-side exposure light 195 to the image-side exposure light 197, which forms the microscopic pattern of the mask 194 on the wafer 198 at the above projection magnification and with well-suppressed aberration. The image-side exposure light 197, as illustrated in the enlarged view in the lower part of FIG. 19, converges at a predetermined numerical aperture NA (=sin(xcex8)) on the wafer 198 to form the image of the microscopic pattern on the wafer 198. When the microscopic pattern is successively transferred onto mutually different shot areas (areas to become one chip or plural chips) in the wafer 198, the substrate stage 199 is stepped along the image plane of the projection optical system to change the position of the wafer 198 relative to the projection optical system 196.
The above-stated projection exposure apparatus using the KrF excimer laser as a light source, which is presently becoming mainstream, has high resolving power, but it is technologically difficult to form a pattern image of not over 0.15 xcexcm thereby, for example.
The projection optical system 196 has the limit of resolution determined from a trade-off between the optical resolution and the depth of focus originating in exposure wavelength (used in exposure). The resolution R and the depth of focus DOF of patterns resolved by the projection exposure apparatus are expressed by the Rayleigh""s formula as indicated by Eq. (1) and Eq. (2) below.
R=k1(xcex/NA) xe2x80x83xe2x80x83(1) 
DOF=k2(xcex/NA2) xe2x80x83xe2x80x83(2) 
In these equations, xcex is the exposure wavelength, NA the numerical aperture on the image side to indicate brightness of the projection optical system 196, and k1 and k2 are constants determined by development process characteristics of the wafer 198 etc., which are normally values of about 0.5 to 0.7.
A potential way for improvement in the resolution to decrease the resolution R is xe2x80x9cemployment of higher NAxe2x80x9d to increase the numerical aperture NA, but there is a limit of evolution in the employment of higher NA over a certain point, because the depth of focus DOF of the projection optical system 196 has to be kept at a value over a certain level in practical exposure. It is thus seen from these Eqs. (1), (2) that xe2x80x9cshortening of wavelengthxe2x80x9d to decrease the exposure wavelength xcex is eventually necessary for the improvement in the resolution.
There, however, arises a significant issue with progression in the wavelength shortening of the exposure wavelength. The issue is that there exists no glass material for the lenses constituting the projection optical system 196. Most of glass materials have transmittances close to 0 in the deep ultraviolet region and fused silica is available at present as a glass material produced for the exposure apparatus (the exposure wavelength of about 248 nm) by a special production method. The transmittance of this fused silica is also lowered quickly at the exposure wavelengths of not more than 193 nm.
It is very difficult to develop a practical glass material in the region of exposure wavelengths of not more than 150 nm corresponding to microscopic patterns having the line widths of 0.15 xcexcm or below. The glass material to be used in the deep ultraviolet region also needs to satisfy plural conditions including durability, index uniformity, optical strain, workability, and so on, as well as the transmittance, which makes it doubtful whether there exists a practical glass material or not.
As described above, the conventional projection exposure methods and projection exposure apparatus need to decrease the exposure wavelength down to about 150 nm or less in order to form the patterns having the line widths of 0.15 xcexcm or below on the wafer. Against it, there exists no practical glass material in this wavelength region at present, and thus no pattern has been allowed to be formed in the line width of 0.15 xcexcm or below on the wafer.
U.S. Pat. No. 5,415,835 discloses the technology of forming the microscopic pattern by two-beam interference exposure, and this two-beam interference exposure permits formation of the pattern in the line width of 0.15 xcexcm or below on the wafer.
The two-beam interference exposure will be explained referring to FIG. 15. In FIG. 15 the two-beam interference exposure is effected as follows; laser light L151 from laser 151, which has coherence and which is a bundle of parallel rays, is split into two beams, laser beams L151a, L151b, by half mirror 152 and the two split beams are reflected by respective plane mirrors 153a, 153b so as to make the two laser beams (parallel beams with coherence) intersect at a certain angle in the range greater than 0 but less than 90xc2x0 on the surface of wafer 154, thereby forming interference fringes at the intersecting portion. A microscopic periodic pattern according to the light intensity distribution of the interference fringes is formed in the wafer 154 by exposing and printing the wafer 154 with the interference fringes (the light intensity distribution thereof).
Supposing the two beams L151a, L151b intersect on the wafer surface as inclined at the same angles on the respective sides with respect to the normal to the surface of the wafer 154, the resolution R in this two-beam interference exposure is expressed by Eq. (3) below.                                                         R              =                              λ                /                                  (                                      4                    ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                    θ                                    )                                                                                                        =                                                λ                  /                  4                                ⁢                NA                                                                                        =                              0.25                ⁢                                  (                                      λ                    /                    NA                                    )                                                                                        (        3        )            
In this equation, R represents the width of each of LandS (lines and spaces), i.e., the width of each of bright part and dark part of the interference fringes. Further, xcex8 indicates the incident angle (absolute value) of each of the two beams to the image plane, and NA=sinxcex8.
When Eq. (3), which is the formula of resolution in the two-beam interference exposure, is compared with Eq. (1), which is the formula of resolution in the normal projection exposure, the resolution R of the two-beam interference exposure is equivalent to that where k1=0.25 in Eq. (1), so that the two-beam interference exposure can achieve the resolution equal to two or more times the resolution of the normal projection exposure with k1=0.5 to 0.7.
For example, when NA=0.6 at xcex=0.248 nm (KrF excimer), we obtain R=0.10 xcexcm, though it is not disclosed in the above U.S. Patent.
Since the two-beam interference exposure basically permits formation of only simple stripe patterns corresponding to the light intensity distribution (exposure amount distribution) of interference fringes, it is not easy to form a circuit pattern of a desired shape on the wafer.
Then above U.S. Pat. No. 5,415,835 suggests formation of isolated lines (line pattern) by multiple exposure in which a resist of the wafer is exposed to the exposure amount distribution corresponding to the interference fringes formed by the two-beam interference exposure and thereafter the normal exposure is carried out using the exposure apparatus and a mask with certain apertures formed therein, thereby providing the wafer with a desired exposure amount distribution.
An object of the present invention is to provide a pattern creating apparatus and a pattern creating method used in the design stage of mask patterns for multiple exposure.
This multiple exposure is exposure steps to expose the same region on the photosensitive substrate to mutually different light patterns without intervention of a developing treatment step.
The present application discloses a pattern creating apparatus comprising: first pattern handling means for preparing and/or displaying first pattern data; second pattern handling means for preparing and/or displaying second pattern data; characteristic parameter handling means for inputting and/or displaying a characteristic parameter for a pattern forming operation; multiple image computing means for carrying out an operation based on the first pattern data and the second pattern data outputted respectively from said first pattern handling means and from the second pattern handling means and based on the characteristic parameter outputted from said characteristic parameter handling means to output forming pattern data of the result of the operation; and forming pattern handling means for displaying said forming pattern data, wherein said first pattern handling means can input at least one of a period, a position, and a gradient of the first pattern, wherein said first pattern handling means displays at least one of a period, a position, and a gradient of the first pattern, wherein said first pattern handling means handles a pattern formed by overlay of plural periodic first patterns, wherein said second pattern handling means displays at least one of a position, a size, and a gradient of the pattern, and wherein said multiple image computing means performs an addition operation to calculate the sum of gradient data at one common position in the first pattern data and the second pattern data and outputs the addition result and wherein said multiple image computing means multiplies the data outputted after the addition operation by a filtering coefficient for each gradient given by said characteristic parameter handling means to obtain gradient data at each position and outputs the gradient data.
The present application also discloses another pattern creating apparatus comprising: first pattern handling means for preparing and/or displaying first pattern data; second pattern handling means for preparing and/or displaying second pattern data; characteristic parameter handling means for inputting and/or displaying a characteristic parameter for a pattern forming operation; forming pattern handling means for inputting and/or displaying final forming pattern data; and multiple image computing means adapted so that when data is inputted from three handling means out of said four handling means, the multiple image computing means computes and outputs one rest data, wherein said multiple image computing means carries out such an optimization operation as not to contradict with a forming pattern operation process to obtain forming pattern data by an operation based on the first pattern data and second pattern data outputted respectively from said first pattern handling means and from the second pattern handling means and based on the characteristic parameter outputted from said characteristic parameter handling means, and wherein said forming pattern operation process comprises steps of performing an addition operation to calculate the sum of gradient data at one common position in the first pattern data and in the second pattern data, outputting the addition result, multiplying the data outputted after the addition operation by a filtering coefficient for each gradient given by said characteristic parameter handling means to obtain gradient data at each position, and outputting the gradient data.
The present application discloses another pattern creating apparatus comprising: first pattern handling means for preparing and/or displaying first pattern data or/and first pattern image data; second pattern handling means for preparing and/or displaying second pattern data or/and second pattern image data; characteristic parameter handling means for inputting and/or displaying a characteristic parameter for a pattern forming operation; forming pattern handling means for inputting and/or displaying final forming pattern data; image computing means for carrying out an operation of first pattern image data to be generated through an exposure apparatus from the first pattern data and an operation of inversion thereof and for carrying out an operation of second pattern image data to be generated through the exposure apparatus from the second pattern data and an operation of inversion thereof to output the operation result; and multiple image computing means adapted so that when data is inputted from three handling means out of said four handling means, the multiple image computing means computes and outputs one rest data, wherein said multiple image computing means carries out such an optimization operation as not to contradict with a forming pattern operation process to obtain forming pattern data by an operation based on the first pattern data and the second pattern data outputted respectively from said first pattern handling means and from the second pattern handling means and based on the characteristic parameter outputted from said characteristic parameter handling means, and wherein said forming pattern operation process comprises steps of performing an addition operation to calculate the sum of gradient data at one common position in the first pattern data and in the second pattern data, outputting the addition result, multiplying the data outputted after the addition operation by a filtering coefficient for each gradient given by said characteristic parameter handling means to obtain gradient data at each position, and outputting the gradient data.
The present application also discloses a pattern creating method wherein multiple image computing means carries out an operation, using first pattern data prepared by first pattern handling means, second pattern data prepared by second pattern handling means, and a characteristic parameter for a pattern forming operation inputted by characteristic parameter handling means, and outputs forming pattern data of the result of the operation to forming pattern handling means. Further, the present application also discloses another pattern computing method wherein, using data from either three handling means out of data from four handling means including first pattern data prepared by first pattern handling means, second pattern data prepared by second pattern handling means, a characteristic parameter for a pattern forming operation inputted by characteristic parameter handling means, and final forming pattern data prepared by forming pattern handling means, one rest data is computed and outputted.
An exposure method of the present invention is a method of exposing a photosensitive substrate with the mask pattern obtained by making use of either one of the pattern computing apparatus stated above.
Another exposure method of the present invention is a method for exposing a photosensitive substrate with the mask pattern obtained by making use of either one of the pattern computing methods stated above.
An exposure apparatus of the present invention has an exposure mode in which a pattern on a mask is transferred onto a photosensitive substrate by use of either one of the exposure methods described above.
A production method of device according to the present invention has steps of exposing a wafer surface to a pattern on a mask surface by use of the above exposure apparatus and thereafter developing the wafer.
A mask of the present invention is produced by making use of either one of the pattern computing apparatus stated above.
A software program of the present invention is characterized by being programmed based on either one of the computing methods stated above.
A memory medium of the present invention is characterized by storing the above software program.
Another mask pattern creating method of the present invention is a mask pattern creating method comprising: a step of preparing data of a target pattern desired to form after exposure; a step of carrying out a logical operation of predetermined micro-line pattern data and said target pattern data; a step of dividing a surface of a mask pattern into plural types of areas, based on the result of the logical operation; a step of setting a light transmittance or a plurality of light transmittances required or allowed for the types of areas and grouping areas for which one light transmittance can be selected, in each light transmittance; and a step of synthesizing a synthetic pattern from grouped patterns formed in the respective light transmittances, wherein data of the synthetic pattern is used as data of the mask pattern.
Another mask pattern creating apparatus of the present invention is a mask pattern creating apparatus comprising: means for storing data of a target pattern desired to form after exposure and predetermined micro-line pattern data; means for carrying out a logical operation of said micro-line pattern data and target pattern data; means for dividing a surface of a mask pattern into plural types of areas, based on the result of the logical operation; means for setting a light transmittance or a plurality of light transmittances required or allowed for the types of areas and for grouping areas for which one light transmittance can be selected, in each light transmittance; means for synthesizing a synthetic pattern from grouped patterns formed in the respective light transmittances; and means for displaying and/or outputting data of the synthetic pattern as data of the mask pattern.
The above mask pattern creating technology of the present invention is preferably provided with a step or means of determining whether a grouped pattern comprised of the grouped areas satisfies a predetermined mask pattern design rule and revising a grouped pattern not satisfying the design rule so that the grouped pattern satisfies the design rule. Each of the pattern areas divided in the respective light transmittances on the mask pattern satisfies the mask pattern design rule, whereby the shape and light transmittances of the mask pattern can be exposed on the exposed substrate with good repeatability (faithful to setting) and whereby the target pattern can be formed on the exposed substrate with better repeatability.
Another mask pattern creating method of the present invention is a mask pattern creating method comprising: a step of preparing data of a target pattern desired to form after exposure; a step of carrying out a logical operation of predetermined micro-line pattern data and said target pattern data; a step of dividing a surface of a mask pattern into plural types of areas, based on the result of the logical operation; a step of setting a light transmittance or a plurality of light transmittances required or allowed for the types of areas and grouping areas for which one light transmittance can be selected, in each light transmittance; a first revising step of determining whether each of the grouped patterns comprised of the grouped areas satisfies a predetermined mask pattern design rule, and revising a grouped pattern not satisfying the design rule so that the grouped pattern satisfies the design rule; and a step of synthesizing a synthetic pattern from grouped patterns formed in the respective light transmittances and revised if necessary, wherein data of the synthetic pattern is used as data of the mask pattern, said mask pattern creating method further comprising: a second revising step of determining whether the synthetic pattern satisfies said design rule and revising the synthetic pattern if the synthetic pattern does not satisfy the design rule; a selection step carried out when each revising step results in obtaining a plurality of revision results for one grouped pattern or synthetic pattern or when said synthesizing step results in obtaining a plurality of synthesis results and, as a result, if said mask pattern data includes a plurality of mask pattern data, said selection step comprising computing images corresponding to the respective mask pattern data and selecting one of the data, based on the obtained image data.
Another mask pattern creating apparatus of the present invention is a mask pattern creating apparatus comprising: means for storing data of a target pattern desired to form after exposure and predetermined micro-line pattern data; means for carrying out a logical operation of said micro-line pattern data and target pattern data; means for dividing a surface of a mask pattern into plural types of areas, based on the result of the logical operation; means for setting a light transmittance or a plurality of light transmittances required or allowed for the types of areas and for grouping areas for which one light transmittance can be selected, in each light transmittance; first revising means for determining whether each of the grouped patterns comprised of the grouped areas satisfies a predetermined mask pattern design rule and for revising a grouped pattern not satisfying the design rule so that the grouped pattern satisfies the design rule; means for synthesizing a synthetic pattern from the grouped patterns formed in the respective light transmittances and revised if necessary and for outputting data of the synthetic pattern as data of the mask pattern; second revising means for determining whether the synthetic pattern satisfies said design rule and for revising the synthetic pattern if the synthetic pattern does not satisfy the design rule; and means adapted so that when each of said revising means obtains a plurality of revision results for one grouped pattern or synthetic pattern or when said synthesizing means obtains a plurality of synthesis results and, as a result, if said mask pattern data includes a plurality of mask pattern data, said means computes images corresponding to the respective mask pattern data and selects one of the images, based on the obtained image data.
Most of the above mask pattern creating technology of the present invention can be executed by the computer and a data preparing person needs only to prepare and input the data (target pattern data) of the same shape as a pattern desired to form finally on the resist. Generation of the mask pattern data thereafter can be carried out automatically by the computer according to the above procedures, so that the optimal mask pattern can be created efficiently even in the design of large-scale semiconductor integrated circuits.
Since each of the pattern areas divided in the respective light transmittances on the mask pattern is revised so as to satisfy the mask pattern design rule, the shape and light transmittances of the mask pattern can be exposed on the exposed substrate with good repeatability (faithful to setting) and the target pattern can thus be formed on the exposed substrate with better repeatability.